System with multi-location arc threshold comparators and communication channels for carrying arc detection flags and threshold updating

ABSTRACT

A plasma reactor system for processing a wafer in which respective comparators are coupled to the respective RF transient sensors which are coupled in turn to respective RF power application points. The comparators have respective comparison thresholds. The system further includes a controller programmed to updating the respective thresholds of the comparators with respective updated thresholds for different ones of the steps of the process recipe.

TECHNICAL FIELD

The disclosure concerns plasma reactors for processing semiconductorworkpiece, and detection of arcing in such a reactor.

BACKGROUND

Arcing in a plasma reactor during processing of a semiconductorworkpiece or wafer can destroy the workpiece or make unusable, orcontaminate the reactor chamber. Therefore, detection of arcing to stopa plasma reactor from processing further wafers is essential to avoiddamage to a succession of wafers. In physical vapor deposition (PVD)plasma reactors, arc detection has been confined to arcing at thesputter target at the reactor ceiling. Such arc detection has been madeby monitoring the output of the high voltage D.C. power supply coupledto the sputter target at the ceiling. Voltage or current transients canreflect arcing events. While this approach has provided reliableindication of arcing events occurring at or near the sputter target atthe reactor ceiling, it has not provided a reliable indication of arcingat the wafer (wafer level arcing). Detection of wafer level arcing canbe particularly difficult because of RF noise surrounding the wafercaused by RF power applied to the wafer support pedestal and, in somereactors, to RF power applied to an inductive coil on the chamber sidewall. Another challenge is the large dynamic range of transients ornoise caused by RF generator transitions called for by a process recipe,for example. Such transition-induced transients must be distinguishedfrom transients caused by arcing at the wafer level.

Plasma reactors typically have components within the reactor chamberthat are consumed or degraded by their interaction with plasma. In a PVDreactor, the consumables may include the sputter target at the ceiling,an internal side wall coil and a process ring kit surrounding the wafersupport pedestal including the electrostatic chuck (ESC). As suchconsumables degrade or are physically changed, they become moresusceptible to arcing. The problem is how to determine when eachconsumable should be replaced before there is an arc.

SUMMARY

A plasma reactor system for processing a semiconductor wafer comprises areactor chamber and a support pedestal in the chamber for holding aworkpiece, and plural power applicators with respective power generatorscoupled to the power applicators. Respective voltage or currenttransient sensors are coupled to respective ones of the powerapplicators and to the support pedestal. Respective comparators arecoupled to the respective transient sensors, the respective comparatorsassociated with respective comparison thresholds. The system furtherincludes a programmable controller programmed to carry out the steps of:(a) storing a process recipe comprising plural steps; (b) updating therespective thresholds of the respective comparators with respectiveupdated thresholds for different ones of the steps of the processrecipe; and (c) responding to an arc detection flag from one of thecomparators by deactivating the respective power generators. In oneembodiment, the system may further comprise communication channelapparatus coupled between the programmable controller and each of thecomparators. In one embodiment, the controller is programmed to updatethe respective thresholds by transmitting the updated thresholds to therespective comparators through the communication channel apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited embodiments of theinvention are attained and can be understood in detail, a moreparticular description of the invention, briefly summarized above, maybe had by reference to the embodiments thereof which are illustrated inthe appended drawings. It is to be noted, however, that the appendeddrawings illustrate only typical embodiments of this invention and aretherefore not to be considered limiting of its scope, for the inventionmay admit to other equally effective embodiments.

FIGS. 1A and 1B depict a plasma reactor with bipolar and monopolarelectrostatic chucks, respectively, having certain wafer level arcdetection and automatic shutdown features.

FIG. 2 is a schematic diagram depicting an RF current sensor circuit inthe reactor of FIG. 1A.

FIG. 3 is a block diagram of a signal conditioner in the reactor of FIG.1A.

FIG. 4 is a schematic diagram depicting an RF voltage sensor circuit inthe reactor of FIG. 1A.

FIGS. 5A and 5B are schematic diagrams of modifications of theembodiments of FIGS. 1A and 1B, respectively, having a wafer level arcdetecting circuit on an electrostatic chuck and employing a voltagesensor.

FIGS. 6A and 6B are schematic diagrams of modifications of theembodiments of FIGS. 1A and 1B, respectively, having a wafer level arcdetecting circuit on an electrostatic chuck employing a current sensor.

FIGS. 7A and 7B together constitute a flow diagram depicting theoperation of a reactor controller in any of the foregoing embodiments.

FIG. 8 depicts a retrofitting of the arc sensing and communicationfeatures of FIG. 1A into a reactor having a local area network.

FIG. 9 depicts a retrofitting of the arc sensing and communicationfeatures of FIG. 1A into a reactor having a digital input/outputnetwork.

FIG. 10 depicts a retrofitting of the arc sensing and communicationfeatures of FIG. 1A into a reactor having a D.C. safety interlock loop.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. The drawings in the figures are all schematic and not toscale.

DETAILED DESCRIPTION

FIG. 1A depicts a PVD reactor having a system for intelligently sensingarcing at the wafer level. The reactor includes a chamber 100 defined bya cylindrical side wall 102, a ceiling 104 and a floor 106. Within theinterior of the chamber 100 are provided a target 110 mounted on theceiling 104, an RF coil 112 mounted on the side wall 102 and a wafersupport pedestal 114 extending upwardly from the floor 106. A vacuumpump 116 evacuates the chamber 100 through a pumping port 118 in thefloor 106. A process gas supply 119 provides process gas (or gases) forintroduction into the chamber 100.

The wafer support pedestal 114, in one embodiment, may include anelectrostatic chuck (ESC) 122 for holding a semiconductor wafer orworkpiece 120 on a top surface of the pedestal 114. The ESC 122 mayconsist of an insulating layer 124 resting on a conductive base 126. Inthe embodiment of FIG. 1A, the ESC 122 is a bipolar chuck, and there aretwo electrodes 128, 130 in the insulating layer 124, and a conductivecenter pin 132 contacting the back side of the wafer 120. A chuckingvoltage supply 134 imposes opposite but equal D.C. voltages between thecenter pin 132 and the electrodes 128, 130. FIG. 1B depicts a variationof the embodiment of FIG. 1A in which the ESC 122 is a monopolar chuckand there is a single electrode 128 having a diameter corresponding,generally, to that of the workpiece or wafer 120. In the embodiment ofFIG. 1B, the center pin 132 may not be present. Except for thesedifferences, the embodiments of FIGS. 1A and 1B contain commonstructural features, and the description below of these common featureswith reference to FIG. 1A pertains to the embodiment of FIG. 1B as well,but are not repeated for the sake of brevity.

Referring again to FIG. 1A, D.C. power is applied to the sputter target110 by a high voltage D.C. power generator 136. Low frequency RF poweris applied to the coil 112 through an RF impedance match 138 by an RFpower generator 140. The RF power generator 140 is connected to an RFinput of the impedance match 138. In one embodiment, the RF impedancematch 138 may have a low power D.C. input (not shown) in addition to theRF input. In the embodiment of FIG. 1A, RF bias power of a suitablefrequency (such as low frequency and/or high frequency) is applied tothe ESC electrodes 128, 130 through a bias impedance match 142 andblocking capacitors 144, 146 by an RF power generator 148. An RFblocking filter 150 connected between the ESC electrodes and center pin128, 130, 132 and the DC chucking voltage supply 134 isolates thechucking voltage supply 134 from RF power. In the embodiment of FIG. 1B,RF bias power of a suitable frequency (such as low frequency and/or highfrequency) is applied to the single ESC electrode 128 through the biasimpedance match 142 and blocking capacitor 144 by the RF bias powergenerator 148.

Referring again to FIG. 1A, a reactor controller 152 governs operationof all the active elements of the reactor. Specifically, FIG. 1Aindicates the communication of ON/OFF commands from the controller 152to each of the power generators 136, 140, and 148, to the gas supply119, to the vacuum pump 116 and to the ESC chucking voltage supply 134.Although not shown in the drawing of FIG. 1A, other active components ofthe reactor are likewise governed by the controller 152, includingcoolant pumps, lid interlocks, lift pin actuators, pedestal elevationactuators, slit valve opening, wafer handling robotics, for example.

Wafer Level Arc Detection:

Detecting plasma arcing at the wafer is difficult because of thepresence of RF noise and harmonics and because of the large dynamicrange of voltage or current transients at the wafer caused by non-arcingevents (power generator transitions) and by arcing. These problems areovercome by sensing current or voltage changes at the RF bias powerinput to the ESC 122. An RF sensor 154 is placed at (or connected to) anRF conductor 155 (e.g., the inner conductor of a 50 Ohm coaxial cable)running between the RF bias generator 148 and the RF bias impedancematch 142. In one embodiment, the RF sensor 154 is contained inside theimpedance match 142 and is located at an internal coaxial outputconnector (not shown) to which the coaxial cable 155 is connected. TheRF sensor 154 is capable of sensing an RF current or an RF voltage andgenerating a voltage signal proportional to the sensed current (orsensed voltage). The voltage signal is processed by a signal conditioner156 to produce an output signal that has been filtered and peak-detectedand scaled to a predetermined range. An arc detect comparator 158compares the magnitude of the output signal to a predetermined thresholdvalue. If this threshold is exceeded by the output signal, the arcdetect comparator outputs an arc flag to the reactor controller 152. Thereactor controller 152 responds to the arc flag by shutting down activecomponents of reactor such as the power generators 136, 140 and 148.

Referring now to FIG. 2, the sensor 154 may be an RF current sensor. Inthis embodiment, the sensor 154 includes a ferrite ring 160 encirclingthe RF conductor 155 and a conductive (e.g., copper) coil 162 wrappedaround a portion of the ferrite ring 160. One end 162 a of the coil 162may be allowed to float electrically, while the other end 162 b is theoutput terminal of the sensor 154. One advantage of the structure of theferrite ring 160 and coil 162 is that the current through the coil 162is weakly coupled to the RF current through the RF power conductor 155.Therefore, the voltage induced on the coil 162 is attenuated andaccordingly has a smaller dynamic range in response to transients orspikes in the current through the conductor 155. A related feature isthat the weakly coupling limits the amount of power or current drawn bythe sensor 154 from the RF power in the conductor 155. As a result, thesensor 154 places only a negligible load on the RF current in theconductor 155.

FIG. 3 depicts the different functions in the signal conditioner 156.The signal conditioner 156 includes a peak detector 164, an RF filter166 for removing noise and providing a cleaner signal, a scaling circuit168 for providing a predetermined range and a high impedance transducer170 for controlling the signal amplitude range while providing a highimpedance isolation between the output of the signal conditioner 156 andthe sensor 154. One embodiment of the signal conditioner 156 isillustrated in FIG. 2. In the embodiment of FIG. 2, the peak detector164 is depicted as including a diode rectifier 164 a and a capacitor 164b. In other embodiments, the peak detector may include other circuitelements that provide an output level indicative of a true peak value.The RF filter 166 is depicted as a pi-network including a pair of shuntcapacitors 166 a, 166 b and a series inductor 166 c. The scaling circuit168 is depicted in FIG. 2 as voltage divider consisting of a pair ofresistors 168 a, 168 b, whose output voltage is scaled down by the ratioof the resistance of the resistor 168 a to the total resistance of theresistors 168 a and 168 b. The transducer 170 is depicted in FIG. 2 asincluding an operational amplifier 171 that provides an output signalwithin a range (e.g., 0-10 V) determined by the amplifier gain. The gainmay be controlled by a variable feedback resistor 172 connected betweenthe amplifier input and output. The amplifier 171 provides a high inputimpedance that isolates the signal conditioner 156 from a load placed onthe signal conditioner output.

FIG. 4 depicts an embodiment of the sensor 154 for sensing an RF voltageon the RF conductor 155. The sensor consists of a resistor divider 154a, 154 b connected directly between the conductor 155 and ground, theseries resistance of the resistor divider 154 a, 154 b being very high(on the order of megOhms). This prevents any significant power diversionto ground. The resistor 154 a is 10-100 times less resistive than theresistor 154 b, so that the voltage sensed by the peak detector 164 isvery small compared to the voltage on the RF conductor 155. Thisprovides the sensor 154 with a high input impedance to avoid drawing anappreciable current from the RF conductor 155. The signal conditioner156 described above with reference to FIGS. 2 and 3 may also be employedto condition the output signal of the RF voltage sensor 154 of FIG. 4.

FIG. 5A depicts a modification of the embodiment of FIG. 1A in which arcdetection is performed at the ESC electrodes 128, 130. The RF bias powergenerator 148 and RF bias impedance match 142 of FIG. 1A are not shownin the drawing of FIG. 5A, although they may be present if RF bias poweris applied to the ESC electrodes 128, 130. Alternatively, no RF biaspower is applied to the ESC electrodes 128, 130. The sensor 154 of FIG.1A is replaced in FIG. 5A by a voltage sensor 174. The voltage sensor174 is connected across the ESC center pin 132 (that is in contact withthe semiconductor workpiece or wafer 120) and a reference point. Thereference point may either be ground or one of the ESC electrodes 128 or130. The voltage sensor 174 is a differential amplifier, with itsdifferential inputs connected to the center pin 132 and the referencepoint (e.g., ground). Voltage transients on the wafer 120 appear as alarge difference between the inputs of the differential amplifier 174.The output of the amplifier is proportional to this difference, and isfurnished to the signal conditioner 156. The output of the signalconditioner is tested by the arc detect comparator 158 by comparisonwith a predetermined threshold, as in the embodiment of FIG. 1A.

FIG. 5B depicts a similar modification to the embodiment of FIG. 1B, inwhich the sensor 154 of FIG. 1B is replaced in FIG. 5B by thedifferential amplifier 174. In the embodiment of FIG. 5B, the inputs tothe differential amplifier 174 are connected to the single ESC electrode128 and a suitable voltage reference such as ground. The RF bias powergenerator 148 and RF bias impedance match 142 of FIG. 1B are not shownin the drawing of FIG. 5B, although they may be present if RF bias poweris applied to the ESC electrode 128. Alternatively, no RF bias power isapplied to the ESC electrode 128. Voltage transients on the wafer 120appear as a large difference between the inputs of the differentialamplifier 174. The output of the amplifier is proportional to thisdifference, and is furnished to the signal conditioner 156. The outputof the signal conditioner is tested by the arc detect comparator 158 bycomparison with a predetermined threshold, as in the embodiment of FIG.1A.

FIG. 6A illustrates a variation of the embodiment of FIG. 5A in which acurrent sensor 176 replaces the voltage sensor 174. The current sensor176 includes a ferrite ring 178 around the center conductor 132 and aconductive winding 180 around the ring 178. One end 180 a of the winding180 is the output of the current sensor 176 and is connected to theinput of the signal conditioner 156. FIG. 6B illustrates a similarvariation of the embodiment of FIG. 5B in which a current sensor 176′replaces the voltage sensor 174. The current sensor 176′ includes aferrite ring 178′ around the conductor connected to the single ESCelectrode 128, and a conductive winding 180′ around the ring 178. Oneend 180 a′ of the winding 180′ is the output of the current sensor 176′and is connected to the input of the signal conditioner 156.

Referring again to FIG. 1A, a second RF sensor 184 is coupled to an RFpower conductor 185 connected between the RF generator 140 and the RFimpedance match 138 for the side wall coil 112. The second RF sensor 184may be an RF current sensor, as in FIG. 2, or an RF voltage sensor, asin FIG. 4. The output of the second RF sensor 184 is applied to a secondsignal conditioner 186 that may be the same type of circuit as thesignal conditioner 156 of FIGS. 2 and 3. A second arc detect comparator188 compares the output of the signal conditioner with a certainthreshold value to determine whether an arc has occurred. If an arc hasoccurred, the comparator 188 generates an arc flag that is sent to thecontroller 152. A third sensor 190 is coupled to the output of the D.C.power generator 136. The output of the third sensor 190 may be appliedto a third signal conditioner 192. A third arc detect comparator 194compares the output of the signal conditioner 192 with a certainthreshold to determine whether an arc has occurred. Its output, an arcflag, is transmitted to the process controller 152.

The controller 152 may include a memory 152 a for storing a sequence ofinstructions and a microprocessor 152 b for executing thoseinstructions. The instructions represent a program that may bedownloaded into the controller memory 152 a for operating the reactor.In accordance with one feature, the program requires the controller 152to shut off the power generators 136, 140, 148 in response to receipt ofan arc flag from any of the arc detect comparators 158, 188 or 194. Thisprogram will be discussed in greater detail in a later portion of thisspecification.

Operation of the Process Controller:

Operation of the process controller 152 of FIG. 1A is depicted in theflow diagram of FIGS. 7A AND 7B. The process recipe may be downloadedinto the controller memory 152 a (block 300 of FIGS. 7A AND 7B). Thereactor component history (e.g., the number of use hours for eachconsumable in the reactor) may also be loaded into the controller memory152 a (block 302). The controller then starts the process in the reactor(block 304). For the current process step, the controller 152 notes theRF power settings called for by the recipe (i.e., the RF power appliedto the ESC 122 and the RF power applied to the coil 112. From thesepower settings, the controller 152 predicts an RF noise levelencountered by each of the sensors 154, 184 and 190. For each sensor,the controller 152 determines from the noise level an appropriate arcdetection comparison threshold for each of the comparators 158, 188 and194 (block 306 of FIGS. 7A AND 7B). For the particular sensor, a sensedvoltage (or current) level exceeding the assigned threshold isconsidered to be an arc event. Optionally, the controller 152 may alsodefine a warning level threshold that is below the arc detectionthreshold.

After the comparison threshold has been defined for each of the sensors154, 184, 190, each threshold is revised in accordance with the age ofthe associated reactor consumable components (block 308). This may bedone in accordance with historical data representing typical lifetimesof each consumable component in the reactor. For example, the sensor 154detects arc events closest to the wafer 120. These are most likelyaffected by the condition of consumable components closest to the wafer,such as a process ring kit surrounding the ESC (not shown in FIG. 1A),for example. Accordingly, the arc detect comparison threshold for thesensor 154 are revised depending upon the age of the process ring kit.Likewise, the sensor 184 detects arc events at the side wall coil 112.Therefore, the thresholds chosen for the sensor 184 are revised basedupon the age of the coil 112, for example. Typically, this revisioncauses the threshold to increase with consumable age or hour usage,because as the consumable wears and its surface becomes rougher duringexposure to plasma, it tends to experience or promote more RF noise andharmonics. This revision of the arc detection threshold based upon agemay be performed based upon empirical data representing the histories ofa large sample of the consumable component.

In one embodiment, the next step is to determine whether the upwardlyadjusted threshold is at or too near the expected voltage or currentlevel of a real arc event (block 310). If so (YES branch of block 310),this fact is flagged (block 311) to the user and/or to the processcontroller 152. In one embodiment, this flag may cause the processcontroller 152 to shut down the reactor. The location of the sensorwhose threshold has become excessive in this way is identified, and thereactor consumables closest to that detector are identified to the useras being due for replacement.

Provided the adjusted thresholds are not excessive (NO branch of block310), they are then sent to the arc detection comparators 158, 188 and194 for use during the current process step (block 312). From theprocess recipe, the controller 152 can identify the specific times ofoccurrence of process-mandated transients (block 314), such as theactivation or deactivation of an RF power generator. During theperformance of the current process step, the controller 152 monitorseach of the arc detection comparators 158, 188 and 194 for arc flags(block 316). Each of the comparators 158, 188, 194 constantly comparesthe output of the respective signal conditioner 156, 186, 192 with thethreshold received from the controller 152 for the current process step.Whenever the signal conditioner output exceeds the applicable threshold,the comparator transmits an arc flag to the controller 152. Thecontroller 152 may sample the comparator outputs at a rate of 30 MHz,for example. For each sample of each comparator 158, 188, 194, adetermination is made whether an arc flag has issued (block 318). If noflag is detected (NO branch of block 318), then the controller 152determines whether the current process step has been completed (block320). If not (NO branch of block 320), the controller 152 returns to themonitoring step of block 316. Otherwise (YES branch of block 320) thecontroller 152 transitions to the next process step in the recipe (block322) and loops back to the step of block 306.

If an arc flag is detected (YES branch of block 318), then it isdetermined whether the sensed voltage or current transient merelyexceeded the warning threshold or whether it exceeded the arc thresholdlevel (block 324). This is determined from the contents of the flagissued by the particular comparator. If it was a warning level only (YESbranch of block 324), then the controller 152 records the event andassociates the event with the current wafer (block 326). The controller152 then determines whether the number of warnings for the current waferis excessive (block 328). If the number of warnings for that waferexceeds a predetermined number (YES branch of block 328), a flag isissued (block 330) and the controller 152 may shut down the reactor.Otherwise (NO branch of block 328), the controller returns to the stepof block 316.

If the arc flag was for a full arc event in which the arc threshold wasexceeded (NO branch of block 324), then a determination is made (block332) as to whether it coincided with a power transition time identifiedin the step of block 314. If so (YES branch of block 332), the flag isignored as a false indication (block 334) and the controller loops backto the monitoring step of block 316. Otherwise (NO branch of block 332),the arc flag is treated as valid. The controller 152 uses the contentsof the arc flag to identify and record in memory the location of thesensor that sensed the arc event (block 338). The controller issues“OFF” commands to each of the power generators 136, 140 and 148 (block340). The arc flag may embody digital information identifying theparticular comparator that issued the arc flag. This information isoutput by the controller 152 to a user interface, which can correlatesensor location with consumable components (block 342). This feature canenable the user to better identify consumable components in the reactorchamber that need to be changed. For example, if the controller 152determines that the arc flag was issued by the comparator 188, then itidentifies the consumable component closest to the RF power monitored bythe comparator, namely the side wall coil 112. For an arc flag issued bythe comparator 158, the closest consumable components are thosesurrounding the wafer, particularly the process ring kit, and thecontroller 152 would associate such an arc flag with the process ringkit, for example. For an arc flag issued from the comparator 194, therelevant component is the ceiling target, and the controller wouldassociate such an arc flag with the ceiling target. Thus, the controller152 in one embodiment can provide the user different lists of possiblecandidate consumables for replacement for different arc flag events.

The process depicted in FIGS. 7A AND 7B includes, in one embodiment,dynamic adjustment of the arc detection comparison threshold for eachstep in the plasma process. The threshold is further adjusted based uponconsumable component age. The controller 152 updates the thresholds ineach of the comparators 158, 188, 194 as often as necessary. By suchdynamic adjustment of the comparison thresholds, the sensitivity of eachcomparator 158, 188, 194 is optimized by seeking the minimum thresholdthat can be used in the environment of a particular wafer process step.The threshold is adjusted downwardly whenever noise conditions (forexample) improve, and is adjusted upwardly when noise level increases,due to an increase in RF power level, for example. Such a thresholdincrease avoids false arc indications that can arise when the noiselevel approaches the arc detection threshold level. In an embodiment,the process of FIGS. 7A AND 7B further includes performing arc locationidentification and corresponding identification of the likeliestconsumable components involved in the arc event. The controller 152communicates this information to the user, to facilitate easiermanagement of consumables and more accurate selection of consumablesneeding replacement.

In one embodiment, the process of FIGS. 7A AND 7B is embodied insoftware instructions downloaded into the controller memory 152 a. Inthis embodiment, therefore, all the intelligent actions are performed bythe controller 152, while the arc detection comparators simply perform acomparison function. However, in another embodiment, the arc detectioncomparators 158, 188, 194 may include their own internal processors andmemories, enabling them to perform some of the functions in the processof FIGS. 7A AND 7B.

Retrofit Control and Communication:

The process of FIGS. 7A AND 7B involves frequent two-way communicationbetween the controller 152 and each of the arc detection comparators158, 188, 194. The controller 152 periodically transmits updatedcomparison threshold values to particular ones of the comparators 158,188, 194, different values being downloaded to different comparators.The comparators 158, 188, 194 transmit arc flags whenever an arc isdetected. The arc flag includes the identity of the individualcomparator that issued it. The controller further transmits shutdown(ON/OFF) commands to the power generators 136, 140 and 148 in responseto a valid arc flag from any of the arc detection comparators 158, 188,194. It is intended that the arc detection features of FIG. 1A (asimplemented in the process of FIGS. 7A and 7B) be installed on plasmareactors already operating in the field. For reactors already installedin the field, installation onto each reactor of a custom communicationnetwork to meet each of the foregoing communication needs would beprohibitively costly. To reduce costs, communication systems alreadyexisting on such reactors are exploited. In some cases, the existingcommunication systems are able to meet and facilitate all of thecommunication needs of the arc detection features of FIGS. 1 and 7.

In some reactors, a local area network (LAN) is provided in which thecontroller communicates via the LAN with every active device and sensoron the reactor. FIG. 8 illustrates the structure of such a LAN in areactor of the type depicted in FIG. 1A. For each active device to begoverned by the controller 152, an interface device is coupled to it.The interface device converts received digital commands to actions thatshut down the active device. For example, in FIG. 8, interface devices355, 357, 359 are connected to respective power generators 136, 140,148. The interface devices are capable of shutting down the generatorsin response to received digital commands. A local area network (LAN) 360is provided. The LAN is a multiple conductor communication channel orcable having multiple I/O ports 361, 362, 363, 364, 365, 366, 367, whichmay be implemented as multiconductor connectors. Each device that is tocommunicate on the LAN 360 has a memory and limited processingcapability that permits it to store and issue a unique address on theLAN 360. Thus, each control interface 355, 357, 359 and each comparator158, 188, 194 has conventional process circuitry that responds to LANprotocols and stores its own device address. Each device 158, 188, 194,355, 357, 359 on the LAN responds only to received communications thatare addressed to its device address. Furthermore, each device attachesits device address to its data transmissions on the LAN. Each of thedevices 158, 188, 194, 355, 357, 359 is coupled to the LAN 360 at aunique one of the ports 361, 362, 363, 364, 365, 366, 367 via its ownmulticonductor cable 371, 372, 373, 374, 375, 376, 377, respectively. Onreactors already installed in the field having such a LAN, there may beno comparators 158, 188, 194. Therefore, the arc detection systemcommunication features of FIG. 1A are realized in such a reactor byidentifying spare (unused) ports on the existing LAN 360 (e.g., theports 363, 365 and 366) and connecting the comparators 158, 188, 194 tothem in the manner depicted in FIG. 8.

The device addresses of all the devices on the LAN 360 (i.e., thecomparators 158, 188, 194 and the control interfaces 355, 357, 359) maybe intelligently assigned by the controller 152 upon activation of theLAN 360, using conventional techniques. In the system of FIG. 8, thecontroller 152 carries out the process of FIGS. 7A AND 7B by sending anindividual communication addressed to an individual comparator withinstructions to download a certain threshold value, for example. Eachcomparator responds to an arc event by transmitting a communicationaddressed to the controller 152 and containing the comparator's deviceaddress and a message signifying occurrence of an arc event. Thecontroller 152 can respond to a valid arc event by transmitting acommunication addressed to each of the power generator controlinterfaces 355, 357, 359 containing a command to shut down thecorresponding generator. The location of the sensor that caused the arcflag to be issued is deduced by the controller 152 from the deviceaddress of the corresponding arc detect comparator. The controller 152can provide this information to the user at a user interface 153 of thecontroller 152.

In other reactors, no LAN is provided or available, and instead a customcommunication digital input/output (DI/O) network is provided asdepicted in FIG. 9. In the DI/O network of FIG. 9, each devicecommunicates with the controller 152 (and vice versa) over acommunication channel dedicated to that device. The DI/O network onpre-existing reactors employs respective DI/O relays 401, 402, 404, 406that individually communicate with the controller 152, and monitorindividual safety points. Specifically, for example, the DI/O relay 401signals whenever a lid 101 of the chamber 100 is opened, the DI/O relay402 signals whenever the RF power cable to the side wall coil isdisconnected, the DI/O relay 404 signals whenever the RF bias powercable is disconnected and the DI/O relay 406 signals whenever the D.C.power cable to the ceiling target is disconnected. The controller 152receives the signals from these relays at inputs A, B, D, and F, asindicated in the drawing of FIG. 9. The controller 152 transmitsshutdown (ON/OFF) commands to each of the power generators 136, 148 and140 via dedicated communication channels J, K and L, as indicated inFIG. 9.

The communication features of FIG. 1A may be implemented in the DI/Onetwork of FIG. 9 provided there are three DI/O relays that can bespared for use with the arc detect comparators 158, 188 and 194. Asshown in the example of FIG. 9, pre-existing DI/O relays 403, 405 and407 are appropriated for connection to the outputs of the arc detectcomparators 188, 158 and 194, respectively. Each time one of the arcdetect comparators 158, 188 or 194 issues an arc flag, the DI/O relayattached to it signals the controller 152. The controller 152 deducesthe identity of the arc detect comparator that issued the arc flag fromthe location of the wire or channel carrying the signal. Thisinformation may be furnished to the controller's user interface 153 foruse in managing consumable replacement.

Earlier model reactors currently installed in the field may have neithera LAN nor a DI/O network. In such reactors, the arc detection system ofFIG. 1A may be implemented in a basic form by exploiting a 24 voltsafety interrupt circuit provided on such reactors. This circuit ensuresimmediate shut down of the power generators whenever the chamber lid isopened or whenever a power cable connection to the chamber isinterrupted. Referring to FIG. 10, the power generator 136 has aninterlock 501, the power generator 148 has an interlock 502 and thepower generator 140 has an interlock 503. Each generator 136, 148 and140 can operate only if its interlock constantly senses a 24 Volt DCpotential on a circuit conductor 504. The circuit conductor 504 connectsall of the interlocks 501, 502, 503 in series with a 24 VDC supply 506.The series circuit conductor 504 is interrupted by several simple switchrelays 510, 512, 514, 516, 518, 520 and 522. Therefore, each relay byitself can sever the series connection of the 24 volt supply 506 to thegenerator interlocks 501, 502, 503, thereby shutting down the reactor.The relay 510 opens its connection whenever the chamber lid 101 isopened. The relay 512 opens its connection whenever the RF power cableconnection to the side wall coil 112 is interrupted. The relay 516 opensits connection whenever the RF power cable to the ESC 122 isinterrupted. The relay 522 opens its connection whenever the RF powercable connection to the ceiling target is interrupted. The chamber 100may be automatically shut down in response to arc detection by any ofthe three arc detect comparators 158, 188 and 194 provided there arethree spare relays connected in series along the circuit conductor 504and available to accept the outputs of respective ones of thecomparators 158, 188 and 194. FIG. 10 shows that three such relays,namely the relays 514, 518 and 520, may be connected to the outputs ofthe comparators 188, 158 and 194, respectively. Whenever any one of thecomparators 188, 158, 194 senses a voltage (or current) exceeding itspredetermined threshold, it issues an arc flag in the form of a voltagethat causes the corresponding relay (514, 518 or 520, respectively) toopen its connection. This interrupts the 24 volt circuit of theconductor 504, causing each of the interlocks 501, 502, 503 to disablethe associated power generator (136, 148 and 140, respectively).

While the embodiment of the RF impedance match 138 illustrated in FIG.1A has a single RF input and an RF output, in another embodiment the RFimpedance match 138 may have, in addition, a low power D.C. input (notshown in the drawings). In such a case, an additional arc sensor andthreshold comparator of the type described above may be coupled to theunillustrated low power D.C. input of the RF impedance match 138.

While the reactor of FIG. 1A or 1B has been described as detecting anarc based upon the output of a single one of the various sensors 154,184, 190, etc., the decision may instead be based upon the outputs ofseveral (or possibly all) of the sensors. For example the controller 152of the embodiment of FIG. 1, 8 or 9 has been described as responding toan arc event based upon the output of any single one of the sensors 154,184 or 190 through the corresponding comparator 158, 186 or 194,respectively. However, in one embodiment, the controller 152 of FIG. 1,8 or 9 is programmed to combine the outputs of at least two (or more) ofthe threshold comparators 158, 186, and make a decision based upon thecombined signals. The output signals may be combined by the processor152 through a linear, polynomial, or more complex mathematical function.In this case, the controller 152 would be programmed to respond to thecombined signal to determine whether an arc was detected or to determinewhether to shut down the reactor. In yet another embodiment, theindividual outputs of the sensors 154, 184, 190 may be combined beforebeing processed by a threshold comparator. The individual output signalsfrom at least two of the sensors 154, 184, 190 may be combined through alinear, polynomial, or more complex mathematical function. The resultingcombined signal is then fed to a single comparator (e.g., the comparator186), and the output of that single comparator is fed to the controller152.

While the foregoing is directed to embodiments of the invention, otherand further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. A plasma reactor system, comprising: a reactor chamber and a supportpedestal in the chamber for holding a workpiece; plural powerapplicators; plural power generators, at least respective ones of saidplural power generators coupled to at least respective ones of saidplural power applicators; plural voltage or current sensors, at leastrespective ones of said plural voltage or current sensors coupled tosaid at least respective ones of said power applicators and to saidsupport pedestal; plural comparators, at least respective ones of saidplural comparators coupled to the at least respective ones of saidvoltage or current sensors, said at least respective ones of saidcomparators associated with respective comparison thresholds; aprogrammable controller programmed to carry out the steps of: (a)storing a process recipe comprising plural steps; (b) updating therespective thresholds of the at least respective ones of saidcomparators with respective updated thresholds for different ones of thesteps of said process recipe; and (c) responding to an arc detectionflag from one of said comparators by deactivating said at leastrespective ones of said plural power generators; communication channelapparatus coupled between said programmable controller and each of saidat least respective ones of said comparators, wherein said controller isprogrammed to (a) update the respective thresholds by transmitting saidupdated thresholds to the at least respective ones of said comparatorsthrough said communication channel apparatus and (b) receive arcdetection flags from said at least respective ones of said comparatorsthrough said communication channel apparatus; respective on/off controlinterfaces coupled to said at least respective ones of said plural powergenerators, said communication channel apparatus being further coupledbetween said programmable controller and said respective on/off controlinterfaces; and wherein each of said comparators is responsive to aunique device address, and wherein said controller is programmed to senda respective updated threshold to the corresponding comparator bytransmitting the device address of the corresponding comparator with theupdated threshold on said communication channel apparatus.
 2. The systemof claim 1 wherein each of said on/off control interfaces is associatedwith a device address and wherein said programmable controller isfurther programmed to deactivate said power generators by transmittingdeactivation commands on said communication channel apparatus withrespective device addresses of said control interfaces.
 3. The system ofclaim 2 further comprising a user interface coupled to said programmablecontroller, said programmable controller being further programmed toinfer locations of arc flags from device addresses accompanying arcflags received on said communication channel apparatus, and to conveysaid locations to said user interface.
 4. The system of claim 2 whereinsaid communication channel apparatus comprises a local area network. 5.The system of claim 1 wherein said support pedestal comprises anelectrostatic chuck having at least one of a chucking electrode or acontact rod for contacting the backside of the workpiece, and whereinsaid sensor coupled to said workpiece support comprises a voltage sensorcoupled to sense a voltage or current transient on one of said contactrod or said chucking electrode.
 6. The system of claim 1 wherein saidsupport pedestal comprises an electrostatic chuck having at least achucking electrode, said system further comprising a power generator andan impedance match coupled between said power generator and saidchucking electrode by a power conductor, said sensor coupled to saidworkpiece support comprising a voltage or current sensor coupled to saidpower conductor.
 7. The system of claim 6 wherein said voltage orcurrent sensor coupled to said power conductor comprises a conductivering around said power conductor and a coil wound around said ring, oneend of said coil being coupled to the corresponding comparator.
 8. Thesystem of claim 1, further comprising: respective sensor relays, some ofsaid relays being coupled to outputs of said at least respective ones ofsaid comparators; wherein said communication channel apparatuscomprises: (a) respective channels dedicated to communication of arcflags from respective ones of said sensor relays to said controller; and(b) respective channels dedicated to communication of shutdown commandsfrom said controller to said at least respective ones of said powergenerators of said reactor.
 9. The system of claim 1, wherein saidcommunication channel apparatus further comprises: respective channelsdedicated to communication of updated thresholds from said processor torespective ones of said comparators.
 10. A plasma reactor system,comprising: a reactor chamber and a support pedestal in the chamber forholding a workpiece; plural power applicators; plural power generators,at least respective ones of said plural power generators coupled to atleast respective ones of said plural power applicators; plural voltageor current sensors, at least respective ones of said plural voltage orcurrent sensors coupled to said at least respective ones of said powerapplicators and to said support pedestal; plural comparators, at leastrespective ones of said plural comparators coupled to the at leastrespective ones of said sensors, said at least respective ones of saidcomparators associated with respective comparison thresholds; on/offcontrol apparatus connected between said respective comparators and saidpower generators; a programmable controller programmed to update therespective thresholds of the at least respective ones of saidcomparators with respective updated thresholds for different steps of aprocess recipe; communication channel apparatus coupled between saidprogrammable controller and each of said at least respective ones ofsaid comparators; wherein each of said at least respective ones of saidcomparators is responsive to a unique device address, and wherein saidcontroller is programmed to send a respective updated threshold to thecorresponding comparator by transmitting the device address of thecorresponding comparator with the updated threshold on saidcommunication channel apparatus.
 11. The system of claim 10 wherein saidon/off control apparatus comprises: an interlock electrical seriescircuit comprising: (a) relays coupled to sense interruption ofrespective safety connections; and (b) power generator interlocks fordisabling respective ones of said power generators upon interruption ofsaid interlock series circuit; and said at least respective ones of saidcomparators being coupled to respective ones of said relays.
 12. Thesystem of claim 10 wherein said support pedestal comprises anelectrostatic chuck having at least one of a chucking electrode or acontact rod for contacting the backside of the workpiece, and whereinsaid sensor coupled to said workpiece support comprises a voltage sensorcoupled to sense a voltage or current transient on one of said contactrod or said chucking electrode.
 13. The system of claim 10 wherein saidsupport pedestal comprises an electrostatic chuck having at least achucking electrode, said system further comprising a power generator andan impedance match and a power conductor coupled between said powergenerator and said chucking electrode, said sensor coupled to saidworkpiece support comprising a voltage or current sensor coupled to saidpower conductor.
 14. The system of claim 13 wherein said voltage orcurrent sensors coupled to said power conductor comprises a conductivering around said power conductor and a coil wound around said ring, oneend of said coil being coupled to the corresponding comparator.